How to disable JBPM persistence?

[sakella1986]

I have an existing JBPM project and JPA persistence is enabled. I would like to disable the JBPM persitence functionality.
I tried removing all the tables from Persitence.xml file and it is not working.

<class>org.jbpm.services.task.audit.impl.model.AuditTaskImpl</class>
<class>org.jbpm.services.task.audit.impl.model.BAMTaskSummaryImpl</class>
<class>org.jbpm.services.task.audit.impl.model.TaskEventImpl</class>

org.drools.persistence.info.SessionInfo
org.jbpm.persistence.processinstance.ProcessInstanceInfo
org.drools.persistence.info.WorkItemInfo
org.jbpm.persistence.correlation.CorrelationKeyInfo
org.jbpm.persistence.correlation.CorrelationPropertyInfo
org.jbpm.runtime.manager.impl.jpa.ContextMappingInfo

<class>org.jbpm.services.task.impl.model.AttachmentImpl</class>
<class>org.jbpm.services.task.impl.model.BooleanExpressionImpl</class>
<class>org.jbpm.services.task.impl.model.CommentImpl</class>
<class>org.jbpm.services.task.impl.model.CompletionBehaviorImpl</class>
<class>org.jbpm.services.task.impl.model.ContentDataImpl</class>
<class>org.jbpm.services.task.impl.model.ContentImpl</class>

<class>org.jbpm.services.task.impl.model.DeadlineImpl</class>
<class>org.jbpm.services.task.impl.model.DeadlinesImpl</class>
<class>org.jbpm.services.task.impl.model.DelegationImpl</class>
<class>org.jbpm.services.task.impl.model.EmailNotificationHeaderImpl</class>
<class>org.jbpm.services.task.impl.model.EmailNotificationImpl</class>
<class>org.jbpm.services.task.impl.model.EscalationImpl</class>
<class>org.jbpm.services.task.impl.model.FaultDataImpl</class>
<class>org.jbpm.services.task.impl.model.GroupImpl</class>
<class>org.jbpm.services.task.impl.model.I18NTextImpl</class>
<class>org.jbpm.services.task.impl.model.LanguageImpl</class>
<class>org.jbpm.services.task.impl.model.NotificationImpl</class>
<class>org.jbpm.services.task.impl.model.OrganizationalEntityImpl</class>
<class>org.jbpm.services.task.impl.model.PeopleAssignmentsImpl</class>
<class>org.jbpm.services.task.impl.model.PresentationElement</class>
<class>org.jbpm.services.task.impl.model.ReassignmentImpl</class>
<class>org.jbpm.services.task.impl.model.TaskDataImpl</class>
<class>org.jbpm.services.task.impl.model.TaskDefImpl</class>
<class>org.jbpm.services.task.impl.model.TaskImpl</class>
<class>org.jbpm.services.task.impl.model.UserImpl</class>

Could someone provide steps to disable JPA persistence so that I dont need to use any of the tables and improve performance. Rightnow we are using HSQL in-memory database for JBPM with hibernate and JAVA EE CDI framework.

I would like to use PostgresSQL for this. What is the recommended database for JBPM?